Fluxes for the treatment of light alloys



Patented Feb. 14, 1950 '"Manchester;England, as'signorto MagnesiumElektron LimitedgLondon, England, a British company NdjDrawing.v.;.App1mamma ,am.26,.misz semi No: 7.1!],763. 'iIn'GreatBritainAygu'st;29; l946 12 .Claims.

invention -relatesto fluxes forthe treatment I of light alloysconsisting of -magnesium hbase 'alloys containing rare earth metals, and

tains substantially no magnesium chloride. {For dthis :purpose Ihaveendeavoured to develop a =flux which -contains .a :mixture of'chlorides .-(which'3[s.term..aflprotectivevbase) having-a sufiicientlylow melting pointe-to-eenable the flux to prevent burning of themetal'and to provide,

together with a suflicientlquantity of inspissating ia entsutor enable..th8ifll=.1Xf.t0l':h&Ve the required iscosityrrawpastyviscous; coverinon ithebmetal. c- -lna.ctherawordslhavazendeavoured toi inspissate amixture ..of .chlorides .-.not,.containing magnesium chloride in amanner in which it has.;previouslyabeenuproposed':to.einspissate.zchloride mixtures consistinglargely ofsmagne'siumachldride. I have, however, found that theinspissation of chloride mixtures not containing magnesium chloride isaccompanied by certain difiiculties. For example, attempts to inspissatea chloride mixture solely by means of an addition of magnesia, result ina tendency to liquation and dry top-effects, that is to say the fluxcover on top of the molten metal is too dry near to its upper surface,and appears to consist mainly of magnesia insufficiently wetted by thechlorides. These difficulties are apparently due to the poor wettingcapacity for MgO of chloride mixtures not containing magnesium chloride.

These difficulties can be overcome by prefusing the magnesia with thechloride mixture but this results in a flux, the composition of whichmust be adjusted somewhat critically to achieve the required degree ofinspissation, and which is barely satisfactory in its ability toextinguish burning magnesium.

Accordingly I have attempted to inspissate these chloride mixtures withcalcium fluoride.

The composition of these fluxes appeared to be very critical in so faras compositions tending to be somewhat fluid showed the pronouncednon-wetting effects to be expected in the absence of magnesium chloride,whereas attempts to 55 .20 The use of "sdiu.m"'and "potassium* fluorideovercome this-difiiculty by'increasing' the amount or thecalciumfluoride until the "flux" 'was ,:so -viscous- -as-to-be--incapab1e" of"showing non' wettingiJcharacteri ticsmroduced: fluxes'gwhichewere 5aitoo dry sforesatisfactery.gprotection :of the emetal .tagainstoxidation. 'flihetxrange of composition abetween, fluxes-showing qthenon-wetting attendency and-thoser whiohaarentoo; dry. isx-itooz narrow.iorasatisfactory :rcom-mercial. productiona: of-; such lfluxes-eandmoreover tdzhe ipptimum .a.calcium s fluoride; acontent rvariestwithtemperature of, the ametalv zunderet-reatment.

Attempts to use-.;calcium :fluoridel andimagnesia atg ether ;;saveefiuxes gqpOSSessihg -to vsome extent ethe r-disadvantages 1:.associated with sthe separate use ofv both these inspissating agents.

"The -use of ;:strontium and "barium fluorides also produceddisadvantages'similar to"thosei.ac-

companying the use'of'calcium fluoride.

gives rise; to introduction of "small amountsfof sodium and traces"of-potassiumintothe'metal nbqth sofewlhichuaiieimbjefltmnablajnaddition to non-wetting difficulties.

The us of nma'gnesium ilfiuoride 'was :zinitially QQQXlSldBI'Bd1impractitable; not 'onlyv-beca-use ituis sine-re. costly l-than-sanyeof,"lihe fluorides :above .e-mentioned; abut more particularly: because it.:-is

- ..well-:.known that rqmagnesi-um v fluoride will react with the rareearth metals in the same way as magnesium chloride.

I have now made the surprising discovery that unlike the fluorides ofsodium, potassium, calcium, strontium, or barium, magnesium fluoride issubstantially insoluble in certain chloride mixtures not containingmagnesium chloride and I have used this discovery to make fluxes whichare very satisfactory for use with alloys containing rare earth metals.I inspissate such chloride mixtures with magnesium fluoride and becausethe latter is practically insoluble in the chloride mixtures non-wettingdoes not arise. Furthermore, when the flux melts the particles ofmagnesium fluoride are readily wetted and coated with the protectivebase in which they do not dissolve and the magnesium fluoride is therebyprotected from contact with the rare earth metals in the alloy and sodoes not react therewith.

The flux may, however, contain a minor proportion of inspissating agentsother than magnesium fluoride. Some small amount of ma nesium chloridemay be tolerated in the flux but this should not exceed 2% and ispreferably less than 0.5%.

According to the present invention therefore,

a flux suitable for the treatment of the aforesaid light alloys issubstantially free from magnesium chloride and consists essentially ofat least two chlorides of the alkali metals and alkaline earth metals,other than magnesium, these chlorides in the absence of inspissatingagents have a liquidus temperature not greater than 610 C., the fluxalso containing a sufficient quantity of one or more inspissating agentsto enable the flux to provide a pasty viscous covering on the moltenmetal, and at least 75% of the inspissating agents consisting ofmagnesium fluoride.

I find in particular that mixtures of calcium,

potassium, and sodium chlorides are suitable for inspissation bymagnesium fluoride especially in the following percentages of thechloride mixture(s) Per cent Calcium chloride 40-70 Potassium chloride6-30 Sodium chloride Q. 24-40 Examples of inspissated flux compositionswhich we have found satisfactory are as follows:

CaClz 41 25.5 49 NaCl 26 23.5 KCl 9 47 BaClz 7 .5 SIC12 7.5 MgFz 24 2020 In these examples the figures indicate percentages by weight of thcompositions.

Magnesium base alloys containing one or more rare earth metals can betreated with fluxes made in accordance with the invention with regularproduction of finished alloys having at least equal freedom from tracesof chloride contamina- 4 tion as commonly produced magnesium base alloyscontaining aluminium.

I claim:

1. An inspissated fluxsuitable for the treatment of magnesiumalloys-containing-a rare earth metal, which flux is substantiallyfree'from magnesium chloride and consists of at least two chlorides ofthe alkali metals and alkaline earth metals, other than magnesium, whichchlorides when in mixture alone have a liquidus temperature not greaterthan 610 C., the balance of the flux being a quantity of inspissatingagent such as to provide a pasty viscous covering on the molten metal,and at least of the inspissating agent consisting of magnesium fluoride,the quantity of magnesium fluoride being about 20% by weight of theflux.

2. A flux as claimed in claim 1 wherein the chlorides consist of thechlorides of calcium, po-

tassium and sodium, in the following percentages of the total chloridemixture:

Per cent Calcium chloride 40-70 Potassium chloride 6-30 Sodium chloride24-40 EDWARD FREDERICK EMLEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,121,292 Haughton et a1. June21, 1938 2,327,065 Reimers Aug. 17, 1943 2,396,604. Reimers Mar. 12,1946 FOREIGN PATENTS I Number Country Date 342,586 Great Britain Feb. 5,1931 403,891 Great Britain Jan. 4, 1934 489,700 Great Britain Aug. 6,1938 OTHER REFERENCES Marande, Materials and Methods, February 1946, pp.418-424.

1. AN INSPISSATED FLUX SUITABLE FOR THE TREATMENT OF MAGNESIUM ALLOYSCONTAINING A RARE EARTH METAL, WHICH FLUX IS SUBSTANTIALLY FREE FROMMAGNESIUM CHLORIDE AND CONSISTS OF AT LEAST TWO CHLORIDES OF THE ALKALIMETALS AND ALKALINE EARTH METALS, OTHER THAN MAGNESIUM, WHICH CHLORIDESWHEN IN MIXTURE ALONE HAVE A LIQUIDUS TEMPERATURE NOT GREATER THAN610*C., THE BALANCE OF THE FLUX BEING A QUANTITY OF INSPISSATING AGENTSUCH AS TO PROVIDE A PASTY VISCOUS COVERING ON THE MOLTEN METAL, AND ATLEAST 75% OF THE INSPISSATING AGENT CONSISTING OF MAGNESIUM FLUORIDE,THE QUANTITY OF MAGNESIUM FLUORIDE BEING ABOUT 20% BY WEIGHT OF THEFLUX.